The technical field generally relates to SCR aftertreatment systems for internal combustion engines. SCR aftertreatment systems are effective at treating engine NOx emissions with a high conversion of NOx. SCR aftertreatment systems operate with the addition of urea or NH3 (reductant) to the system, and react the reductant with the NOx, to reduce the NOx. The addition of any excess reductant to the system consumes the reductant without the benefit of NOx reduction, increasing the operating cost of the system. Additionally, the excess reductant may be slipped from the system, causing undesired emissions, odors, and/or irritation. Where it is not allowable for the reductant to slip but control of the reductant addition amounts is not acceptably precise, a cleanup oxidation catalyst downstream of the SCR catalyst may be utilized, which can reduce reductant slip amounts but increases system acquisition and maintenance costs. Nevertheless, precise control of the reductant addition is difficult. Many SCR catalyst formulations exhibit NH3 storage and release dynamics, and the determination of the instantaneous engine-out NOx amount is difficult to determine in a commercially viable mobile application. Further, most currently available NOx sensors have cross-sensitivity to NH3, complicating the direct measurement of NOx and the separation of NOx from NH3 detection. Therefore, further technological developments are desirable in this area.